The present invention relates to flame retardant corrosion resistant polyethylene films, with the films preferably being in a laminated structure which shrinks or contracts upon application of heat to provide a tight fitting enveloping protective enclosure about large articles such as vehicles or other equipment during periods of non-use. These new films have the functions of providing both flame retardancy while simultaneously preserving the function of corrosion protection and being arranged to be incorporated in a laminate structure to provide tight-fitting enveloping protective enclosures about metallic articles when enclosed or packaged in these films. An anti-static component as well as an ultra-violet inhibitor may be added to the films of the invention without sacrifice of any of their desirable properties.
Flame retardancy in both films and textiles has become a necessity for certain articles with a number of applications being mandated by law. Similar mandates along with some requirements have been established by and for certain air carriers in connection with the fabrics employed within their interiors, and for many exhibition procedures. Flame retardancy in films is achieved by incorporating additives such as antimony oxides, certain borax salts and halogenated organics, all of which retard the flame propagation. A standard has been established as NFPA-701 and laboratories have been certified that approve articles and issue a certificate of conformance.
Paper and films that incorporate flame retardants have been available for many years. Paper coatings comprising corrosion inhibitors (hereafter sometimes referred to as xe2x80x9cVCIxe2x80x9d) were initially developed about 1950. Selected VCI corrosion inhibitors in films that function as a source for volatile corrosion inhibitors became available commercially about 1980. Certain features of these two concepts along with certain other added features comprise the primary elements of the present invention. Among the added elements are the selection of flame retardant-corrosion resistant polyethylene films that shrink or contract upon application of heat, and also selection of certain of these films to be employed in a multi-layer laminate form.
The problem of blending the flame retardant (hereafter FR) chemicals with suitable VCI chemicals has been overcome with careful selection of components having preferred molecular structures. Chemicals commonly used for flame retardancy are mutually antagonistic when combined with typical VCI chemicals, with resulting reactions which either negate or substantially reduce their utility. In addition, many of the flame retardant chemicals are corrosive to metals and accordingly cannot be used in packaging metals. In the present arrangement, a multi-layer laminate such as a three-layer laminate with the interior or article-contacting film being blended with a corrosion inhibitor, and with the outer or exterior film containing flame retardant chemicals is especially useful. Additionally, the thermal properties of the films may be selected so that the resultant laminate is both flame retardant and corrosion resistant, while at the same time possessing the property of shrinking upon application of heat to provide tight-fitting enveloping protective enclosures. Certain polyethylene films, which are commercially available, possess the property of shrink capability for shrink-wrapping applications. In certain military applications, it may be both necessary and practical to utilize flame contact with the film in order to achieve the thermal shrinking. In this connection, it is believed that certain films prepared pursuant to the present invention are in compliance with the standards established by the National Fire Protection Association (NFPA). In certain applications, it may be desirable to utilize graded amounts of flame retardants and corrosion inhibitors in the individual layers, with a desirable arrangement being to provide a higher concentration of flame retardant compounds in the outer two films of a four-film laminate, with the vapor phase corrosion inhibitors being primarily concentrated in the inner two layers.
In accordance with the present invention, it has been found that with a proper selection of films incorporating VCI chemicals and flame retardant chemicals along with the selection of multi-layer laminates of these films, a dual function film is obtained that provides flame retardancy and provides complete and long term corrosion protection to articles packaged therein. In multi-layer co-extruded films, the interior film is preferably blended with the corrosion inhibitor, while the exterior or outer film layer is blended with a flame retardant chemical.
The most effective flame retardant compositions are produced when colloidal antimony pentoxide (Sb2O5) is blended with halogen containing compounds preferable at a mole ratio of about 3:1. Antimony trioxide (Sb2O3) may also be utilized effectively in the same mole ratio.
Many brominated compounds ranging in percent bromine from a high of 75% bromine to a low of 36% are available commercially, with certain of these compounds being available from Great Lakes Chemical Corp. of West Lafayette, Indiana. Combinations of halogenated phosphate and phosphated esters with phosphorous content ranging from 6.5% to 17% are also available. Suitable flame retardant chemicals in this group are also available from Dow Chemical under the trade designation xe2x80x9cDerkanesxe2x80x9d, from Interplastic under the trade designation xe2x80x9cCo-Rezynxe2x80x9d, and from Ashland under the trade designation xe2x80x9cHetronxe2x80x9d and from Reichold under the trade designations xe2x80x9cDionxe2x80x9d and xe2x80x9cAtlacxe2x80x9d. Volatile corrosion inhibitor chemicals (VCI) that are effective are amine and ammonium salts, such as cyclohexylammonium benzoate, ethanolamine benzoate, amine salts of sebacic acid, and ammonium benzoate. Corrosion inhibitors that are also effective are sodium molybdate, sodium sebacate, and sodium nitrite.
Careful selection and mixing of the components is essential as the manufacturing process includes exposure to two separate heat cycles and it is imperative that the VCI chemicals and flame retardant chemicals be retained and do not react or otherwise form reaction products while undergoing both heat cycles.
In most cases, optimum flame retardant performance in a halogen/antimony system is attained when the halogen and antimony are present in a molar ratio such that there are three moles of halogen present per mole of antimony. Mole ratios between about 2.5:1 to 3.5:1 may be useful. For example, decabromodiphenyl oxide has a bromine content of 83%, and a melting point of about 300xc2x0 C.-315xc2x0 C. which makes it particularly inert through both heat cycles. Antimony oxide reacts with halogen acids to form volatile compounds in the presence of high heat and flame to form volatile compounds that terminate combustion reactions and extinguish flames. When the decabromodiphenyl oxide (DBO) was used in a formulation with antimony pentoxide in a ratio of 3 parts DBO to 1.3 part antimony pentoxide and thereafter blended with about 1 part corrosion inhibitor chemicals, a suitable final blend was obtained for the initial twin screw masterbatch preparation. Other high melting halogenated compounds are also available that have the low volatility necessary for the heat processing operations. A melting point of at least 200xc2x0 C. is desired in both the flame retardant and VCI chemicals when used in applications pursuant to the present invention.
Therefore, it is a primary object of the present invention to provide an improved flame retardant film which incorporates corrosion inhibitors, thereby providing the dual function of flame retardancy and corrosion protection.
It is yet a further object of the present invention to provide an improved flexible film with flame retardant properties, and wherein the film contains corrosion inhibitors which serve to provide an added element of protection to metallic components with surfaces that are reasonably likely to come into contact with the film.
It is still a further object of the present invention to provide an improved flexible polyethylene film in laminate form with flame retardant and corrosion inhibiting properties, and wherein the inner film in the laminate contains corrosion inhibitors, and wherein the outer or exterior film in the laminate contains a flame retardant component, and wherein the polyethylene film possesses the property of shrinking upon exposure to thermal energy.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification and appended claims.
In accordance with one preferred embodiment of the present invention, masterbatch formulation techniques are utilized to prepare a masterbatch of flame retardant and VCI components held within a low density polyethylene matrix. Thereafter, the masterbatches are mixed and/or blended as appropriate to a working formulation in order to produce films in accordance with the present invention.
The following examples provide a description of the steps to be undertaken in the preparation and/or fabrication of masterbatches and films pursuant to the present invention.
A twin screw extruder operating at a temperature range of 300xc2x0 F. to 350xc2x0 F. was used to produce a masterbatch of flame retardant and VCI chemicals in low density polyethylene. These masterbatches were further blended with the polyethylene and blown films were produced at a temperature range of 325xc2x0 F. to 350xc2x0 F.